The body paragraphs.
You are the most important
The target audience is not a physical part of a business letter. The target audience is what directs the content of the letter. When writing a business letter, understanding who (the target audience) you are communicating with is as important as the information you are conveying.
A business plan is an outline for your business. The executive summary is the section of a strategic business plan that the U.S. Business Administration say is the most important part of the plan.
I receive approximately 30 business plans per week: from my point-of-view, as a potential investor, the management team is the most important part of a business plan followed by the cash flow statement.
Kernel.
It is part of the business letter that authenticates statements and shows the signature of the letter sender.
Art, clip-art, or other illustrations are not part of the business letter, they would be attachments to the letter, listed at the end of the letter as 'enclosure(s)'.
That part of the letter is called the salutation or greeting.
A business letter is one which has been sent from a business using their letterhead. This is part of official business correspondence in accordance with company policy.
The first step to any new business is a business plan. You need to decide what you are gong to sell, who will buy it, and what your costs will be to start. Having a business plan is the most important part of a business start up.
Parts of a business letter that are part of a personal letter:date,salutation,body,complimentary closesignature
That would be the "body" of the letter.